A new in vitro preparation, the rat aortic-arch and aortic nerve, has been developed to examine the role of the electrical and mechanical properties of baroreceptors in normotensive (NTR) and spontaneously hypertensive (SHR) rats. The fiber content of the aortic nerve will be examined following appropriate nerve section to determine the numbers and types of afferent and efferent fibers. The structure of the vessel walls and receptor endings of NTR and SHR will be investigated with light microscopy and electron microscopy. The element content, particularly Na and K of the extracellular spaces, smooth muscle cells, and receptor ending, of NTR and SHR, will be examined using energy dispersive x-ray analysis. Tissues will be prepared using lyophilized and frozen techniques.